In my case, error 4 means “The cause was a user-mode read resulting in no page being found.”

As commenter “LittleAncientForestKami” explains, maybe not rocket science, but since I had no idea how to figure this out, really appreciated.

Update:
So, I thought I’d figure out what “rip” and “rsp” meant. “rsp” is probably a little hard to use, but “rip” is the address of the instruction where the crash occured, and you can figure out what function it points to using this technique described by StackOverflow user qrtt1:

Dump the addresses of the crashing application by saying “objdump -d ProcessNameThatCrashed | less” (where “ProcessNameThatCrashed” is the name of the crashing app)

Search for the address in ‘less’ by typing “/”, then entering the address name (in this case, the address I’m searching for is ‘81473d0’).

A few (or maybe many) lines up from the line matching the address in question, you should see the name of the function that crashed:

“brew install boost” (without the quotes). Notice errors. Try updating brew by doing a ‘brew update’. Failures. Notice by looking at /Users/<userid>/Library/Logs/Homebrew/boost/01.bootstrap.sh that “brew” is at version 0.95 on my machine. Research brew and see it’s on version 1.4.0. Reinstall Brew as though it’s never been installed (even though it is). Notice install says success despite printing a couple of errors during the install. Use “sudo rm /usr/local/share/man/man1/brew.1” and “sudo rm /usr/local/share/doc/homebrew” and re-install brew: /usr/bin/ruby -e “$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)” to fix.

Retry “brew install boost”. Success! And brew has installed the latest Boost (1.66.0); under the old version of brew it was trying to install version Boost 1.59.0.